Re: [PATCH v2 2/9] security: allow finer granularity in permitting copy-up of security xattrs

[Amir Goldstein]

On Mon, Feb 5, 2024 at 8:25 PM Stefan Berger <stefanb@xxxxxxxxxxxxx> wrote:
>
> Copying up xattrs is solely based on the security xattr name. For finer
> granularity add a dentry parameter to the security_inode_copy_up_xattr
> hook definition, allowing decisions to be based on the xattr content as
> well.
>
> Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>

For ovl part

Acked-by: Amir Goldstein <amir73il@xxxxxxxxx>

> ---
>  fs/overlayfs/copy_up.c            | 2 +-
>  include/linux/evm.h               | 5 +++--
>  include/linux/lsm_hook_defs.h     | 3 ++-
>  include/linux/security.h          | 4 ++--
>  security/integrity/evm/evm_main.c | 2 +-
>  security/security.c               | 7 ++++---
>  security/selinux/hooks.c          | 2 +-
>  security/smack/smack_lsm.c        | 2 +-
>  8 files changed, 15 insertions(+), 12 deletions(-)
>
> diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> index 8586e2f5d243..de20fe9333c0 100644
> --- a/fs/overlayfs/copy_up.c
> +++ b/fs/overlayfs/copy_up.c
> @@ -114,7 +114,7 @@ int ovl_copy_xattr(struct super_block *sb, const struct path *oldpath, struct de
>                 if (ovl_is_private_xattr(sb, name))
>                         continue;
>
> -               error = security_inode_copy_up_xattr(name);
> +               error = security_inode_copy_up_xattr(old, name);
>                 if (error < 0 && error != -EOPNOTSUPP)
>                         break;
>                 if (error == 1) {
> diff --git a/include/linux/evm.h b/include/linux/evm.h
> index 36ec884320d9..840ffbdc2860 100644
> --- a/include/linux/evm.h
> +++ b/include/linux/evm.h
> @@ -31,7 +31,7 @@ extern void evm_inode_post_setxattr(struct dentry *dentry,
>                                     const char *xattr_name,
>                                     const void *xattr_value,
>                                     size_t xattr_value_len);
> -extern int evm_inode_copy_up_xattr(const char *name);
> +extern int evm_inode_copy_up_xattr(struct dentry *dentry, const char *name);
>  extern int evm_inode_removexattr(struct mnt_idmap *idmap,
>                                  struct dentry *dentry, const char *xattr_name);
>  extern void evm_inode_post_removexattr(struct dentry *dentry,
> @@ -118,7 +118,8 @@ static inline void evm_inode_post_setxattr(struct dentry *dentry,
>         return;
>  }
>
> -static inline int  evm_inode_copy_up_xattr(const char *name)
> +static inline int evm_inode_copy_up_xattr(struct dentry *dentry,
> +                                         const char *name)
>  {
>         return 0;
>  }
> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index 185924c56378..7dd61f51d84a 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -163,7 +163,8 @@ LSM_HOOK(int, 0, inode_listsecurity, struct inode *inode, char *buffer,
>          size_t buffer_size)
>  LSM_HOOK(void, LSM_RET_VOID, inode_getsecid, struct inode *inode, u32 *secid)
>  LSM_HOOK(int, 0, inode_copy_up, struct dentry *src, struct cred **new)
> -LSM_HOOK(int, -EOPNOTSUPP, inode_copy_up_xattr, const char *name)
> +LSM_HOOK(int, -EOPNOTSUPP, inode_copy_up_xattr, struct dentry *src,
> +        const char *name)
>  LSM_HOOK(int, 0, kernfs_init_security, struct kernfs_node *kn_dir,
>          struct kernfs_node *kn)
>  LSM_HOOK(int, 0, file_permission, struct file *file, int mask)
> diff --git a/include/linux/security.h b/include/linux/security.h
> index d0eb20f90b26..9fc9ca6284d6 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -387,7 +387,7 @@ int security_inode_setsecurity(struct inode *inode, const char *name, const void
>  int security_inode_listsecurity(struct inode *inode, char *buffer, size_t buffer_size);
>  void security_inode_getsecid(struct inode *inode, u32 *secid);
>  int security_inode_copy_up(struct dentry *src, struct cred **new);
> -int security_inode_copy_up_xattr(const char *name);
> +int security_inode_copy_up_xattr(struct dentry *src, const char *name);
>  int security_kernfs_init_security(struct kernfs_node *kn_dir,
>                                   struct kernfs_node *kn);
>  int security_file_permission(struct file *file, int mask);
> @@ -980,7 +980,7 @@ static inline int security_kernfs_init_security(struct kernfs_node *kn_dir,
>         return 0;
>  }
>
> -static inline int security_inode_copy_up_xattr(const char *name)
> +static inline int security_inode_copy_up_xattr(struct dentry *src, const char *name)
>  {
>         return -EOPNOTSUPP;
>  }
> diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
> index cc7956d7878b..2555aa4501ae 100644
> --- a/security/integrity/evm/evm_main.c
> +++ b/security/integrity/evm/evm_main.c
> @@ -896,7 +896,7 @@ void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
>                 evm_update_evmxattr(dentry, NULL, NULL, 0);
>  }
>
> -int evm_inode_copy_up_xattr(const char *name)
> +int evm_inode_copy_up_xattr(struct dentry *src, const char *name)
>  {
>         if (strcmp(name, XATTR_NAME_EVM) == 0)
>                 return 1; /* Discard */
> diff --git a/security/security.c b/security/security.c
> index 0144a98d3712..ee63863c1dc0 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2596,6 +2596,7 @@ EXPORT_SYMBOL(security_inode_copy_up);
>
>  /**
>   * security_inode_copy_up_xattr() - Filter xattrs in an overlayfs copy-up op
> + * @src: union dentry of copy-up file
>   * @name: xattr name
>   *
>   * Filter the xattrs being copied up when a unioned file is copied up from a
> @@ -2606,7 +2607,7 @@ EXPORT_SYMBOL(security_inode_copy_up);
>   *         if the security module does not know about attribute, or a negative
>   *         error code to abort the copy up.
>   */
> -int security_inode_copy_up_xattr(const char *name)
> +int security_inode_copy_up_xattr(struct dentry *src, const char *name)
>  {
>         struct security_hook_list *hp;
>         int rc;
> @@ -2618,12 +2619,12 @@ int security_inode_copy_up_xattr(const char *name)
>          */
>         hlist_for_each_entry(hp,
>                              &security_hook_heads.inode_copy_up_xattr, list) {
> -               rc = hp->hook.inode_copy_up_xattr(name);
> +               rc = hp->hook.inode_copy_up_xattr(src, name);
>                 if (rc != LSM_RET_DEFAULT(inode_copy_up_xattr))
>                         return rc;
>         }
>
> -       return evm_inode_copy_up_xattr(name);
> +       return evm_inode_copy_up_xattr(src, name);
>  }
>  EXPORT_SYMBOL(security_inode_copy_up_xattr);
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index a6bf90ace84c..ebb8876837c6 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -3530,7 +3530,7 @@ static int selinux_inode_copy_up(struct dentry *src, struct cred **new)
>         return 0;
>  }
>
> -static int selinux_inode_copy_up_xattr(const char *name)
> +static int selinux_inode_copy_up_xattr(struct dentry *dentry, const char *name)
>  {
>         /* The copy_up hook above sets the initial context on an inode, but we
>          * don't then want to overwrite it by blindly copying all the lower
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 0fdbf04cc258..bffca165f07f 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -4873,7 +4873,7 @@ static int smack_inode_copy_up(struct dentry *dentry, struct cred **new)
>         return 0;
>  }
>
> -static int smack_inode_copy_up_xattr(const char *name)
> +static int smack_inode_copy_up_xattr(struct dentry *src, const char *name)
>  {
>         /*
>          * Return 1 if this is the smack access Smack attribute.
> --
> 2.43.0
>